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Abstract Background While growth factors have the potential to halt degeneration and decrease inflammation in animal models, the literature investigating the effect of dosage on human cells is lacking. Moreover, despite the completion of clinical trials using growth differentiation factor‐5 (GDF‐5), no results have been publicly released. Aims The overall objective was to quantitatively assess the effect of three clinically relevant concentrations of GDF‐5 (0.25, 1, and 2 mg) as a therapeutic for disc regeneration. Materials and methods Firstly, this work experimentally determined the effects of GDF‐5 concentration on the metabolic and matrix synthesis rates of human nucleus pulposus (NP) cells. Secondly, in silico modeling was employed to predict the subsequent regenerative effect of different GDF‐5 treatments (± cells). Results This study suggests a trend of increased matrix synthesis with 0.25 and 1 mg of GDF‐5. However, 2 mg of GDF‐5 significantly upregulates oxygen consumption. Despite this, in silico models highlight the potential of growth factors in promoting matrix synthesis compared to cell‐only treatments, without significantly perturbing the nutrient microenvironment. Discussion This work elucidates the potential of GDF‐5 on human NP cells. Although the results did not reveal statistical differences across all doses, the variability and response among donors is an interesting finding. It highlights the complexity of human response to biological treatments and reinforces the need for further human research and personalized approaches. Furthermore, this study raises a crucial question about whether these potential biologics are more regenerative in nature or better suited as prophylactic therapies for younger patient groups. Conclusion Biological agents exhibit unique characteristics and features, demanding tailored development strategies and individualized assessments rather than a one‐size‐fits‐all approach. Therefore, the journey to realizing the full potential of biological therapies is long and costly. Nonetheless, it holds the promise of revolutionizing spinal healthcare and improving the quality of life for patients suffering from discogenic back pain.

Back pain is a global epidemiological and socioeconomic problem affecting up to 80% of people at some stage during their life and is often due to degeneration of the intervertebral disc (IVD). Therapies aimed at restoring the intradiscal space have predominantly focused on delivery of biomaterials, cells, or growth factors, among others, with variable degrees of success. While viral gene delivery strategies have emerged as promising therapeutic options in recent years, these approaches often have off‐target effects and are associated with immunogenicity risks and other comorbidities. Consequently, nonviral methods have gained traction as potential avenues for gene delivery. Herein, enhanced cell‐penetrating peptide (CPP) systems are used to deliver microRNAs in an in vitro and ex vivo model of disc degeneration. The data suggest that nanoparticle complexation of CPPs with (miR‐221‐inhibitor + miR‐149‐mimic) promotes protective effects in nucleus pulposus cells challenged with inflammatory cytokines TNF‐α and IL‐1β. Specifically, increases in matrix deposition, significant decreases in the secretion of an array of inflammatory cytokines, and decreased expression of matrix degradation enzymes MMP13 and ADAMTS5 are observed. These miR‐CPP nanocomplexes can be further employed for targeting of the pericellular matrix space through homing, thus providing a promising approach for therapies of the intradiscal space.

Despite extensive research, targeted delivery of substances to the brain still poses a great challenge due to the selectivity of the blood-brain barrier (BBB). Most molecules require either carrier- or receptor-mediated transport systems to reach the central nervous system (CNS). These transport systems form attractive routes for the delivery of therapeutics into the CNS, yet the number of known brain endothelium-enriched receptors allowing the transport of large molecules into the brain is scarce. Therefore, to identify novel BBB targets, we combined transcriptomic analysis of human and murine brain endothelium and performed a complex screening of BBB-enriched genes according to established selection criteria. As a result, we propose the high-affinity cationic amino acid transporter 1 (SLC7A1) as a novel candidate for transport of large molecules across the BBB. Using RNA sequencing and in situ hybridization assays, we demonstrated elevated SLC7A1 gene expression in both human and mouse brain endothelium. Moreover, we confirmed SLC7A1 protein expression in brain vasculature of both young and aged mice. To assess the potential of SLC7A1 as a transporter for larger proteins, we performed internalization and transcytosis studies using a radiolabelled or fluorophore-labelled anti-SLC7A1 antibody. Our results showed that SLC7A1 internalised a SLC7A1-specific antibody in human colorectal carcinoma (HCT116) cells. Moreover, transcytosis studies in both immortalised human brain endothelial (hCMEC/D3) cells and primary mouse brain endothelial cells clearly demonstrated that SLC7A1 effectively transported the SLC7A1-specific antibody from luminal to abluminal side. Therefore, here in this study, we present for the first time the SLC7A1 as a novel candidate for transport of larger molecules across the BBB.

Abstract Background Blood-brain barrier (BBB) models based on primary murine, bovine, and porcine brain capillary endothelial cell cultures have long been regarded as robust models with appropriate properties to examine the functional transport of small molecules. However, species differences sometimes complicate translating results from these models to human settings. During the last decade, brain capillary endothelial-like cells (BCECs) have been generated from stem cell sources to model the human BBB in vitro. The aim of the present study was to establish and characterize a human BBB model using human induced pluripotent stem cell (hiPSC)-derived BCECs from the hIPSC line SBAD0201. Methods The model was evaluated using transcriptomics, proteomics, immunocytochemistry, transendothelial electrical resistance (TEER) measurements, and, finally, transport assays to assess the functionality of selected transporters and receptor (GLUT-1, LAT-1, P-gp and LRP-1). Results The resulting BBB model displayed an average TEER of 5474 ± 167 Ω·cm2 and cell monolayer formation with claudin-5, ZO-1, and occludin expression in the tight junction zones. The cell monolayers expressed the typical BBB markers VE-cadherin, VWF, and PECAM-1. Transcriptomics and quantitative targeted absolute proteomics analyses revealed that solute carrier (SLC) transporters were found in high abundance, while the expression of efflux transporters was relatively low. Transport assays using GLUT-1, LAT-1, and LRP-1 substrates and inhibitors confirmed the functional activities of these transporters and receptors in the model. A transport assay suggested that P-gp was not functionally expressed in the model, albeit antibody staining revealed that P-gp was localized at the luminal membrane. Conclusions In conclusion, the novel SBAD0201-derived BBB model formed tight monolayers and was proven useful for studies investigating GLUT-1, LAT-1, and LRP-1 mediated transport across the BBB. However, the model did not express functional P-gp and thus is not suitable for the performance of drug efflux P-gp reletated studies.

Direct oral anticoagulants (DOACs) are increasingly used for the treatment of thrombosis. While inhibitors of factor IIa and factor Xa have shown effectiveness, the risk of bleeding remains a significant concern. Recently, direct factor XIa inhibitors—including asundexian and milvexian—have emerged as potential anticoagulation therapies, based on clinical observations that patients with factor XIa deficiencies seldom present with spontaneous bleeding tendencies. The interferences associated with DOACs in routine and specialised coagulation assays are well-described; however, the interferences associated with emerging FXIa inhibitors are largely uncharacterised. Here, we briefly report the impact of asundexian and milvexian in routine coagulation assays using in vitro plasma-based systems. Asundexian and milvexian induce concentration-dependent prolongations in APTT-based assays with curvilinear regressions, which may be suitable for the measurement of pharmacodynamic effects at peak levels ex vivo. We also report differential sensitivities of APTT-based assays—particularly at higher FXIa inhibitor concentrations—highlighting the clinical need for an extensive evaluation of interferences associated with FXIa inhibitors in coagulation assays.

Abstract Background A significant hurdle for potential cell‐based therapies is the subsequent survival and regenerative capacity of implanted cells. While many exciting developments have demonstrated promise preclinically, cell‐based therapies for intervertebral disc (IVD) degeneration fail to translate equivalent clinical efficacy. Aims This work aims to ascertain the clinical relevance of both a small and large animal model by experimentally investigating and comparing these animal models to human from the perspective of anatomical scale and their cellular metabolic and regenerative potential. Materials and Methods First, this work experimentally investigated species‐specific geometrical scale, native cell density, nutrient metabolism, and matrix synthesis rates for rat, goat, and human disc cells in a 3D microspheroid configuration. Second, these parameters were employed in silico to elucidate species‐specific nutrient microenvironments and predict differences in temporal regeneration between animal models. Results This work presents in silico models which correlate favorably to preclinical literature in terms of the capabilities of animal regeneration and predict that compromised nutrition is not a significant challenge in small animal discs. On the contrary, it highlights a very fine clinical balance between an adequate cell dose for sufficient repair, through de novo matrix deposition, without exacerbating the human microenvironmental niche. Discussion Overall, this work aims to provide a path towards understanding the effect of cell injection number on the nutrient microenvironment and the “time to regeneration” between preclinical animal models and the large human IVD. While these findings help to explain failed translation of promising preclinical data and the limited results emerging from clinical trials at present, they also enable the research field and clinicians to manage expectations on cell‐based regeneration. Conclusion Ultimately, this work provides a platform to inform the design of clinical trials, and as computing power and software capabilities increase in the future, it is conceivable that generation of patient‐specific models could be used for patient assessment, as well as pre‐ and intraoperative planning.

Bioactive peptides regulate many physiological functions but progress in discovering them has been slow. Here, the authors use a machine learning framework to predict mammalian peptide candidates from the global and local structure of large-scale tissue-specific mass spectrometry data.

Abstract Background In vitro studies using nucleus pulposus (NP) cells are commonly used to investigate disc cell biology and pathogenesis, or to aid in the development of new therapies. However, lab‐to‐lab variability jeopardizes the much‐needed progress in the field. Here, an international group of spine scientists collaborated to standardize extraction and expansion techniques for NP cells to reduce variability, improve comparability between labs and improve utilization of funding and resources. Methods The most commonly applied methods for NP cell extraction, expansion, and re‐differentiation were identified using a questionnaire to research groups worldwide. NP cell extraction methods from rat, rabbit, pig, dog, cow, and human NP tissue were experimentally assessed. Expansion and re‐differentiation media and techniques were also investigated. Results Recommended protocols are provided for extraction, expansion, and re‐differentiation of NP cells from common species utilized for NP cell culture. Conclusions This international, multilab and multispecies study identified cell extraction methods for greater cell yield and fewer gene expression changes by applying species‐specific pronase usage, 60–100 U/ml collagenase for shorter durations. Recommendations for NP cell expansion, passage number, and many factors driving successful cell culture in different species are also addressed to support harmonization, rigor, and cross‐lab comparisons on NP cells worldwide.

Articular cartilage defects fail to heal spontaneously, typically progressing to osteoarthritis. Bone marrow stimulation techniques such as microfracture (MFX) are the current surgical standard of care; however MFX typically produces an inferior fibro-cartilaginous tissue which provides only temporary symptomatic relief. Here we implanted solubilised articular cartilage extracellular matrix (ECM) derived scaffolds into critically sized chondral defects in goats, securely anchoring these implants to the joint surface using a 3D-printed fixation device that overcame the need for sutures or glues. In vitro these ECM scaffolds were found to be inherently chondro-inductive, while in vivo they promoted superior articular cartilage regeneration compared to microfracture. In an attempt to further improve the quality of repair, we loaded these scaffolds with a known chemotactic factor, transforming growth factor (TGF)-β3. In vivo such TGF-β3 loaded scaffolds promoted superior articular cartilage regeneration. This study demonstrates that ECM derived biomaterials, either alone and particularly when combined with exogenous growth factors, can successfully treat articular cartilage defects in a clinically relevant large animal model.

Abstract Background It is well established that the unique biochemical microenvironment of the intervertebral disc plays a predominant role in cell viability and biosynthesis. However, unless the effect of microenvironmental conditions is primary to a study objective, in vitro culture parameters that are critical for reproducibility are both varied and not routinely reported. Aims This work aims to investigate the local microenvironments of commonly used culture configurations, highlighting physiological relevance, potential discrepancies, and elucidating possible heterogeneity across the research field. Materials and Methods This work uses nutrient‐transport in silico models to reflect on the effect of often underappreciated parameters, such as culture geometry and diffusional distance (vessel, media volume, construct size), seeding density, and external boundary conditions on the local microenvironment of two‐dimensional (2D) and three‐dimensional (3D) in vitro culture systems. Results We elucidate important discrepancies between the external boundary conditions such as the incubator level or media concentrations and the actual local cellular concentrations. Oxygen concentration and cell seeding density were found to be highly influential parameters and require utmost consideration when utilizing 3D culture systems. Discussion This work highlights that large variations in the local nutrient microenvironment can easily be established without consideration of several key parameters. Without careful deliberation of the microenvironment within each specific and unique system, there is the potential to confound in vitro results leading to heterogeneous results across the research field in terms of biosynthesis and matrix composition. Conclusion Overall, this calls for a greater appreciation of key parameters when designing in vitro experiments. Better harmony and standardization of physiologically relevant local microenvironments are needed to push toward reproducibility and successful translation of findings across the research field.

Abstract Back pain is a global epidemiological and socioeconomic problem often associated with intervertebral disc degeneration; a condition believed to initiate in the nucleus pulposus (NP). There is considerable interest in developing early therapeutic interventions to target the NP and halt degeneration. Rat caudal models of disc degeneration have demonstrated significant utility in the study of disease progression and its impact on tissue structure, composition, and mechanical performance. One significant advantage of the caudal model is the ease of access and high throughput nature. However, considerable variability exists across the literature in terms of experimental setup and parameters. The objective of this article is to aid researchers in the design and development of caudal puncture models by providing details and insight into the most reported experimental parameters. Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) guidelines were employed to screen the existing literature and 80 manuscripts met the inclusion criteria. Disc geometry, surgical approaches, effect of needle gauge size to induce degeneration, therapeutic volume, outcome measures, and associated limitations are considered and discussed, and a range of recommendations based on different research questions are presented.

Abstract Background Despite exciting advances in regenerative medicine, cell‐based strategies for treating degenerative disc disease remain in their infancy. To maximize the potential for successful clinical translation, a more thorough understanding of the in vivo microenvironment is needed to better determine and predict how cell therapies will respond when administered in vivo. Aims This work aims to reflect on the in vivo nutrient microenvironment of the degenerating IVD through consolidating what has already been measured together with investigative in silico models. Materials and Methods This work uses in silico modeling, underpinned by more recent experimentally determined parameters of degeneration and nutrient transport from the literature, to re‐evaluate the current knowledge in terms of grade‐specific stages of degeneration. Results Through modeling only the metabolically active cell population, this work predicts slightly higher glucose concentrations compared to previous in silico models, while the predicted results show good agreement with previous intradiscal pH and oxygen measurements. Increasing calcification with degeneration limits nutrient transport into the IVD and initiates a build‐up of acidity; however, its effect is compensated somewhat by a reduction in diffusional distance due to decreasing disc height. Discussion This work advances in silico modeling through a strong foundation of experimentally determined grade‐specific input parameters. Taken together, pre‐existing measurements and predicted results suggest that metabolite concentrations may not be as critically low as commonly believed, with calcification not appearing to have a detrimental effect at stages of degeneration when cell therapies are an appropriate intervention. Conclusion Overall, our initiative is to provoke greater deliberation and consideration of the nutrient microenvironment when performing in vitro cell culture and cell therapy development. This work highlights urgency for robust experimental glucose measurements in healthy and degenerating IVDs, not only to validate in silico models but to significantly advance the field in fully elucidating the nutrient microenvironment and refining in vitro techniques to accelerate clinical translation.

The purpose of this case was to report the impact of early use of high-volume hemofiltration on a previously healthy male admitted after sustaining a high-voltage electrical injury. Initial labs revealed acute kidney injury secondary to rhabdomyolysis with myoglobinuria. The patient required fasciotomies to the three affected extremities and a right above the elbow amputation. Aggressive fluid resuscitation failed to maintain urine output above 20 mL/h. By 24 h, the patient had a 12.8 L positive fluid balance. High-volume hemofiltration was initiated at 60 mL/kg/h using a system with a high cut-off filter for acute kidney injury and volume management. Urine myoglobin was negative by day 3 and serum myoglobin decreased to 221.46 nmol/L. He was extubated on day 5, achieved euvolemia on day 6, and high-volume hemofiltration was discontinued on day 13 with subsequent full renal recovery. He underwent several staged surgeries for burn wound excision and grafting, and the left lower extremity was salvaged. His length of stay was prolonged due to multiple social barriers, but free of sepsis and pneumonia. Early initiation of high-volume hemofiltration with a high cut-off filter helped to expedite removal of acute kidney injury and enable more effective volume management to minimize complications of high-voltage electrical injury and its treatment and likely improve outcomes.

Abstract Background Ex vivo disc organ culture systems have become a valuable tool for the development and pre‐clinical testing of potential intervertebral disc (IVD) regeneration strategies. Bovine caudal discs have been widely selected due to their large availability and comparability to human IVDs in terms of size and biochemical composition. However, despite their extensive use, it remains to be elucidated whether their nutrient microenvironment is comparable to human degeneration. Aims This work aims to create the first experimentally validated in silico model which can be used to predict and characterize the metabolite concentrations within ex vivo culture systems. Materials & Methods Finite element models of cultured discs governed by previously established coupled reaction‐diffusion equations were created using COMSOL Multiphysics. Experimental validation was performed by measuring oxygen, glucose and pH levels within discs cultured for 7 days, in a static compression bioreactor. Results The in silico model was successfully validated through good agreement between the predicted and experimentally measured concentrations. For an ex vivo organ cultured in high glucose medium (4.5 g/L or 25 mM) and normoxia, a larger bovine caudal disc (Cd1‐2 to Cd3‐4) had a central concentration of ~2.6 %O2, ~8 mM of glucose and a pH value of 6.7, while the smallest caudal discs investigated (Cd6‐7 and Cd7‐8), had a central concentration of ~6.5 %O2, ~12 mM of glucose and a pH value of 6.9. Discussion This work advances the knowledge of ex vivo disc culture microenvironments and highlights a critical need for optimization and standardization of culturing conditions. Conclusion Ultimately, for assessment of cell‐based therapies and successful clinical translation based on nutritional demands, it is imperative that the critical metabolite values within organ cultures (minimum glucose, oxygen and pH values) are physiologically relevant and comparable to the stages of human degeneration.

Understanding how the local cellular environment influences cell metabolism, phenotype and matrix synthesis is crucial to engineering functional tissue grafts of a clinically relevant scale. The objective of this study was to investigate how the local oxygen environment within engineered cartilaginous tissues is influenced by factors such as cell source, environmental oxygen tension and the cell seeding density. Furthermore, the subsequent impact of such factors on both the cellular oxygen consumption rate and cartilage matrix synthesis were also examined. Bone marrow derived stem cells (BMSCs), infrapatellar fat pad derived stem cells (FPSCs) and chondrocytes (CCs) were seeded into agarose hydrogels and stimulated with transforming growth factor-β3 (TGF- β3). The local oxygen concentration was measured within the center of the constructs, and numerical modeling was employed to predict oxygen gradients and the average oxygen consumption rate within the engineered tissues. The cellular oxygen consumption rate of hydrogel encapsulated CCs remained relatively unchanged with time in culture. In contrast, stem cells were found to possess a relatively high initial oxygen consumption rate, but adopted a less oxidative, more chondrocyte-like oxygen consumption profile following chondrogenic differentiation, resulting in net increases in engineered tissue oxygenation. Furthermore, a greater reduction in oxygen uptake was observed when the oxygen concentration of the external cell culture environment was reduced. In general, cartilage matrix deposition was found to be maximal in regions of low oxygen, but collagen synthesis was inhibited in very low (less than 2%) oxygen regions. These findings suggest that promoting an oxygen consumption profile similar to that of chondrocytes might be considered a key determinant to the success of stem cell-based cartilage tissue engineering strategies.

There has been significant interest in identifying alternative cell sources and growth factor stimulation to improve matrix synthesis for disc repair. Recent work has identified nasoseptal chondrocytes (NC) as a possible alternative cell source with significant matrix-forming abilities. While various growth factors such as members of the TGFβ superfamily have been explored to enhance matrix formation, no consensus exists as to the optimum growth factor needed to induce cells towards a discogenic phenotype. This study assessed both nucleus pulposus (NP) and NC microtissues of different densities (1000, 2500 or 5000 cells/microtissue) stimulated by individual or combinations of the growth factors TGFβ3, GDF5, and GDF6. Lower cell densities result in increased sGAG/DNA and collagen/DNA levels due to higher nutrient availability levels. Our findings suggest that growth factors exert differential effects on matrix synthesis depending on the cell type. NP cells were found to be relatively insensitive to the different growth factor types examined in isolation or in combination. Overall, NCs exhibited a higher propensity to form extracellular matrix compared to NP cells. In addition, stimulating NC-microtissues with GDF5 or TGFβ3 alone induced enhanced matrix formation and may be an appropriate growth factor to stimulate this cell type for disc regeneration.

Many of the current innovations in instrument design have been focused on making them smaller, more rugged, and eventually field transportable. The ultimate application is obvious, carrying the instrument to the field for real time sample analysis without the need for a support laboratory. Real time data are priceless when screening either biological or environmental samples, as mitigation strategies can be initiated immediately upon the discovery that contaminant metals are present in a location they were not intended to be. Additionally, smaller “handheld” instruments generally require less sample for analysis, possibly increasing sensitivity, another advantage to instrument miniaturization. While many other instruments can be made smaller just by using available micro-technologies (e.g., eNose), shrinking an ICP-MS or AES to something someone might carry in a backpack or pocket is now closer to reality than in the past, and can be traced to its origins based on a component-by-component evaluation. While the optical and mass spectrometers continue to shrink in size, the ion/excitation source remains a challenge as a tradeoff exists between excitation capabilities and the power requirements for the plasma’s generation. Other supporting elements have only recently become small enough for transport. A systematic review of both where the plasma spectrometer started and the evolution of technologies currently available may provide the roadmap necessary to miniaturize the spectrometer. We identify criteria on a component-by-component basis that need to be addressed in designing a miniaturized device and recognize components (e.g., source) that probably require further optimization. For example, the excitation/ionization source must be energetic enough to take a metal from a solid state to its ionic state. Previously, a plasma required a radio frequency generator or high-power DC source, but excitation can now be accomplished with non-thermal (cold) plasma sources. Sample introduction, for solids, liquids, and gasses, presents challenges for all sources in a field instrument. Next, the interface between source and a mass detector usually requires pressure reduction techniques to get an ion from plasma to the spectrometer. Currently, plasma mass spectrometers are field ready but not necessarily handheld. Optical emission spectrometers are already capable of getting photons to the detector but could eventually be connected to your phone. Inert plasma gas generation is close to field ready if nitrogen generators can be miniaturized. Many of these components are already commercially available or at least have been reported in the literature. Comparisons to other “handheld” elemental analysis devices that employ XRF, LIBS, and electrochemical methods (and their limitations) demonstrate that a “cold” plasma-based spectrometer can be more than competitive. Migrating the cold plasma from an emission only source to a mass spectrometer source, would allow both analyte identification and potentially source apportionment through isotopic fingerprinting, and may be the last major hurdle to overcome. Finally, we offer a possible design to aid in making the cold plasma source more applicable to a field deployment.

Propofol, a commonly used sedative in the intensive care unit, is formulated in a 10% lipid emulsion that contributes 1.1 kcals per mL. As a result, propofol can significantly contribute to caloric intake and can potentially result in complications of overfeeding for patients who receive concurrent enteral or parenteral nutrition therapy. In order to avoid potential overfeeding, some clinicians have empirically decreased the infusion rate of the nutrition therapy, which also may have detrimental effects since protein intake may be inadequate. The purpose of this review is to examine the current literature regarding these issues and provide some practical suggestions on how to restrict caloric intake to avoid overfeeding and simultaneously enhance protein intake for patients who receive either parenteral or enteral nutrition for those patients receiving concurrent propofol therapy.

From human health exposure related to environmental contamination to ancient deep-Earth processes related to differentiation of the Earth’s geochemical reservoirs, the adaptability of inductively coupled plasma mass spectrometry (ICP-MS) has proven to be an indispensable standard technique that transcends disciplines. Continued advancements in ICP-MS, including improved auxiliary applications such as laser ablation (LA), ion/liquid chromatography (IC), automated pre-concentration systems (e.g., seaFAST), and improved desolvating nebulizer systems (e.g., Aridus and Apex) have revolutionized our ability to analyze almost any sample matrix with remarkable precision at exceedingly low elemental abundances. The versatility in ICP-MS applications allows for effective interdisciplinary crossover, opening a world of analytical possibilities. In this communication, we discuss the adaptability of geochemical techniques, including sample preparation and analysis, to environmental and biological systems, using Pb isotopes for source apportionment as a primary example.

The intervertebral disc (IVD) relies mainly on diffusion through the cartilaginous endplates (CEP) to regulate the nutrient and metabolites exchange, thus creating a challenging microenvironment. Degeneration of the IVD is associated with intradiscal acidification and elevated levels of pro-inflammatory cytokines. However, the synergistic impact of these microenvironmental factors for cell-based therapies remains to be elucidated. The aim of this study was to investigate the effects of low pH and physiological levels of interleukin-1ß (IL-1β) and tumour necrosis factor-α (TNF-α) on nasal chondrocytes (NCs) and subsequently compare their matrix forming capacity to nucleus pulposus (NP) cells in acidic and inflamed culture conditions. NCs and NP cells were cultured in low glucose and low oxygen at different pH conditions (pH 7.1, 6.8 and 6.5) and supplemented with physiological levels of IL-1β and TNF-α. Results showed that acidosis played a pivotal role in influencing cell viability and matrix accumulation, while inflammatory cytokine supplementation had a minor impact. This study demonstrates that intradiscal pH is a dominant factor in determining cell viability and subsequent cell function when compared to physiologically relevant inflammatory conditions. Moreover, we found that NCs allowed for improved cell viability and more effective NP-like matrix synthesis compared to NP cells, and therefore may represent an alternative and appropriate cell choice for disc regeneration.

Successfully regenerating damaged or diseased bone and other joint tissues will require a detailed understanding of how joint specific environmental cues regulate the fate of progenitor cells that are recruited or delivered to the site of injury. The goal of this study was to explore the role of cyclic tensile strain (CTS) in regulating the initiation of mesenchymal stem cell/multipotent stromal cell (MSC) differentiation, and specifically their progression along the endochondral pathway. To this end, we first explored the influence of CTS on the differentiation of MSCs in the absence of any specific growth factor, and secondly, we examined the influence of the long-term application of this mechanical stimulus on markers of endochondral ossification in MSCs maintained in chondrogenic culture conditions. A custom bioreactor was developed to apply uniaxial tensile deformation to bone marrow-derived MSCs encapsulated within physiological relevant 3D fibrin hydrogels. Mechanical loading, applied in the absence of soluble differentiation factors, was found to enhance the expression of both tenogenic (COL1A1) and osteogenic markers (BMP2, RUNX2, and ALPL), while suppressing markers of adipogenesis. No evidence of chondrogenesis was observed, suggesting that CTS can play a role in initiating direct intramembranous ossification. During long-term culture in the presence of a chondrogenic growth factor, CTS was shown to induce MSC re-organization and alignment, increase proteoglycan and collagen production, and to enhance the expression of markers associated with endochondral ossification (BMP2, RUNX2, ALPL, OPN, and COL10A1) in a strain magnitude-dependent manner. Taken together, these findings indicate that tensile loading may play a key role in promoting both intramembranous and endochondral ossification of MSCs in a context-dependent manner. In both cases, this loading-induced promotion of osteogenesis was correlated with an increase in the expression of the osteogenic growth factor BMP2. The results of this study demonstrate the potent role that extrinsic mechanical loading plays in guiding stem cell fate, which must be carefully considered when designing cell and tissue-engineering therapies if they are to realize their clinical potential.